The RMT union alerted management at South West Trains about ‘members of the public taking pictures of staff without permission', according to a message posted on the RMT news blog.

The union blog informs members: ‘This has been raised at company council level and was informed (sic) by the company that British Transport Police have advised them that this is not against the law to carry this out.

‘To advise that we have now asked for a legal opinion from the union solicitors to see if what BTP are saying us (sic) is correct.

‘As soon as we get a response on this we will update you further.'

Chris Milner, deputy editor of The Railway Magazine, who spotted the blog posting earlier this month, told Amateur Photographer: ‘Railway staff are a vital and important part of the everyday scene, and have been for more than 185 years.

‘The majority of staff are courteous, obliging, happy to engage in conversation, but normally don't mind being photographed doing the job they enjoy.'

Milner, who is also a keen photographer, added: ‘Let's not forget that we are also recording tomorrow's history today.